Yes they are available on some bikes. A few highend offer the travel change like Intense or Titus to name a few, but most are lower end bikes aim to promote versatility most fail, too high shock ratio.
A few people I know who owns these kinds of bike do not change them, they may tried to satisfy the curiosity but usually leave in it's longest travel setting. I did with my Motolite but it was only a one time deal. Why carry the same weight and set the shortest travel.